lower bound = 7

C(9,6,3) = 7

Method of Construction: dynamic programming covering

Lower Bound: Handbook of Combinatorial Designs section on coverings

  1  2  3  4  5  6
  1  2  3  4  5  7
  1  2  3  4  5  8
  1  2  3  4  5  9
  1  2  6  7  8  9
  3  4  6  7  8  9
  1  5  6  7  8  9